Thermodynamic analysis of an innovative transcritical CO_2 parallel Rankine cycle driven by engine waste heat and liquefied natural gas cold

摘要

In this study, to promote the performance of engine waste heat recovery, for the first time, an innovative transcritical CO2 parallel Rankine cycle driven by engine waste heat and liquefied natural gas cold is proposed and studied. Firstly, the thermodynamic analysis including energy and exergy analysis is conducted, and heat transfer requirement analysis for fluids in different working state is presented. Then parametric analysis is conducted, the effects of different parameters on system performance are investigated. According to the results, by adjusting the temperature and pressure of cycle, system performance can be maximized, and with the utilization of liquefied natural gas cold, the entire system achieves the increase of power output of 20%, improvement of thermal and exergy efficiency of 2%. When condensation temperature changes from 20 degrees C to -10 degrees C, system power output has an improvement of 86% (from 103.37 kW to 192.37 kW) while heat transfer area only increases by 25% (from 162.83 m(2) to 218.72 m(2)). Moreover, a performance comparison of system based on CO2 and six widely-used organic fluids is carried out, and results demonstrate that CO2 has better performance than organic fluids. Furtherly, the optimization analysis of system power output is conducted. The results indicate that the proposed system achieves the maximum power output of 205.60 kW, at the same time, the engine power output can be improved by 21.42%. Finally, an exergy destruction analysis is presented, and the results show that the exergy destruction rate of condenser reaches to 70.94% of total exergy destruction due to the large temperature difference between CO2 and liquefied natural gas.